1. Field of the Invention
The present invention relates to a display. More specifically, the present invention relates to a display including a display element such as a liquid crystal display element and an anisotropic scattering film.
2. Description of the Related Art
Liquid crystal displays typified by those in Twisted nematic (TN) mode have been known as a typical example of displays with display performances dependent on a viewing angle (with viewing angle characteristics). The term “with display performances dependent on a viewing angle” means that such devices show different display performances such as contrast ratio, gradation characteristics, and chromaticity between when observed in the front direction (the normal direction of the viewing screen of the display, the direction at a viewing angle of 0°) and when observed in an oblique direction (direction at a viewing angle larger than 0°). It is generally known that these display performances when the device is observed in the oblique direction are inferior to those when observed in the front direction.
In a TN mode liquid crystal display, the contrast ratio gradually decreases as the viewing angle increases in the upper, lower, left, or right direction (in the direction of 3 o'clock, 6 o'clock, 9 o'clock, and 12 o'clock). For example, even if the contrast ratio is 320 when the device is observed in the front direction, the contrast ratio is 10 when observed in the upper direction (direction of 12 o'clock) at a viewing angle of 75°, in the lower direction (direction of 6 o'clock) at a viewing angle of 50°, in the left direction (direction of 9 o'clock) at a viewing angle of 65°, and in the right direction (direction of 3 o'clock) at a viewing angle of 68°. The display color is neutral (not tinged) when observed in the front direction, but the display color is tinged with yellow when observed in the upper, lower, left, or right direction. Particularly when observed in the lower direction, an abnormal phenomenon of a gradation characteristic referred to as a gradation reversal in which negative and positive are reversed in a display image may be observed. Such viewing angle dependency of display performances of the liquid crystal displays results from optical anisotropy of components such as anisotropy of refractive index of liquid crystal molecules, polarization absorption property and polarization transmission property of a polarizing plate, and such viewing angle dependency of the display performances can be said to be inherent characteristics in the liquid crystal displays.
Various methods have been proposed as a method for improving the viewing angle dependency of the display performances of the liquid crystal displays. Examples of methods proposed as such methods include: pixel division methods (including Half Tone Gray Scale method in which one pixel is divided into multiple sections and voltages applied to pixels are changed in certain proportions and Domain Division method in which one pixel is divided into multiple domains and liquid crystal alignment is controlled separately in each domain); display modes such as In-plane switching (IPS) mode in which an electric field is applied to liquid crystals laterally, Multi-domain Vertical Alignment (MVA) mode in which liquid crystal vertically aligned during no voltage application is driven, and Optically Compensated Birefringence (OCB) mode in which a bend aligned cell and a retardation film are combined; and an optical compensation method using a retardation film. It has been also investigated to employ these methods in appropriate combinations, and these methods are adopted in many liquid crystal displays which have been already commercialized.
However, if the above-mentioned pixel division methods or the display modes are adopted, an alignment film, a structure of an electrode and the like, need to be modified, and for this modification, establishment of the production techniques or installation of the production facilities is needed. As a result, the production becomes difficult, and the production costs increase. In these respects, there was room for improvement. Further, its effect of improving the viewing angle dependency is insufficient. Also in the optical compensation method using a retardation film, its effect of improving the viewing angle dependency is limited. For example, an optimal phase difference value for compensating a phase difference of a liquid crystal cell varies between the cases of displaying white and black, and therefore it is impossible to compensate the phase difference of the liquid crystal cell in both black display and white display by the optical compensation method. In addition, the compensation effect attributed to the retardation film is not attained at all in axial azimuths of polarization axes (transmission axis and absorption axis) of a polarizing plate in principle, and the improvement effect is obtained only within the range of specified azimuth angles. In these respects, there was room for improvement.
In addition to the above-mentioned methods, a method of providing a scattering film for averaging outgoing light on the viewing screen side of a liquid crystal display element is known as a method of improving the viewing angle dependency of the display performances of the liquid crystal displays. This method can be applied to all display modes and basically needs no modification of the structure of the display cell. In addition, the effect can be attained during both black display and white display and attained also in the axial azimuth of the polarizing axes of the polarizing plate, which is different from in the above-mentioned optical compensation method using the retardation film.
A diffusion backlight system which emits diffused light is employed as a light source of a commonly used liquid crystal display. Most of liquid crystal display modes or polarizing plates show the best characteristics for vertically incident light. Therefore, light from the diffusion backlight system is collimated as far as possible by a lens film and the like, and is vertically inputted into a liquid crystal display element (liquid crystal cell). As a result, a better effect of improving the viewing angle dependency can be attained, and therefore many technologies concerning this diffusion backlight system have been proposed.
However, a method of obtaining the collimated light simply and effectively has not been established yet, and therefore, a method of using a scattering film for improving the viewing angle dependency is employed actually in combination with the diffusion backlight system, as mentioned above. In such a case, the effect of improving the viewing angle dependency can be attained as mentioned above, but there was room for improvement in that during black display, the scattering film angles part of leakage light, which is obliquely inputted into or outputted from the liquid crystal cell, to the front direction, and thereby light leakage increases in the front direction, which largely reduces the contrast ratio in the front direction. This is because the scattering film has isotropic scattering performances, and therefore the scattering property for transmitting light of the scattering film does not vary so much even if the incidence angle is somewhat changed.
For the above-mentioned circumstances, light control plates produced by irradiating a resin composition consisting of a plurality of compounds, each of which has a refractive index differing from one another and one or more photopolymerizable carbon-carbon double bonds in a molecule, with ultraviolet light from a linear light source within a prescribed angular range, and thereby curing the resin composition (for example, referring to Japanese Kokai Publication No. Sho-63-309902, Japanese kokai Publication No. Sho-64-40903, Japanese Kokai Publication No. Sho-64-40905, Japanese Kokai Publication No. Sho-64-40906, Japanese Kokai Publication No. Sho-64-77001, Japanese Kokai Publication No. Hei-01-147405, Japanese Kokai Publication No. Hei-01-147406, Japanese Kokai Publication No. Hei-02-51101, Japanese Kokai Publication No. Hei-02-54201, Japanese Kokai Publication No. Hei-02-67501, Japanese Kokai Publication No. Hei-03-87701, Japanese Kokai Publication No. Hei-03-109501, and Japanese Kokai Publication No. Hei-06-9714), and liquid crystal displays equipped with such light control plates (for example, referring to Japanese Kokai Publication No. Hei-07-64069 and Japanese Kokai Publication No. 2000-180833) are disclosed. Such light control plates selectively scatter light which enters the plates at a specific angle. Accordingly, it is thought that use of these light control plates can eliminate the above-mentioned reduction in contrast ratio in the front direction to some extent.
However, it is thought that as shown in FIG. 50, in this resin cured part of the light control plate, a plate-like regions 40 having refractive indexes different from those of surrounding regions are formed in parallel with one another in conformity with the length direction of a linear light source 51 located above a light control plate 50 in preparation of the light control plate 50. Therefore, the incidence angle dependency of the scattering property which the light control plate 50 exhibits is hardly recognized when the light control plate 50 is rotated about the A-A axis shown in FIG. 50, along which the plate-like regions 40 having refractive indexes different from those of surrounding regions alternately appear. However, the incidence angle dependency of the scattering property is recognized when rotated about the B-B axis along which the refractive index does not change and is uniform.
FIG. 51 is a diagram schematically showing the incidence angle dependency of the scattering property which the light control plate 50 in FIG. 50 shows. The vertical axis represents a linear transmitting light quantity as an indicator of a scattering degree. The horizontal axis represents an incidence angle. The solid line and the broken line in FIG. 51 represent the case of rotating the light control plate 50 about the A-A axis in FIG. 50 and the case of rotating the light control plate 50 about the B-B axis in FIG. 50, respectively. It is shown by the plus and minus of the incidence angle that the light control plate 50 is rotated in directions opposite to each other.
The linear transmitting light quantity expressed by the solid line in FIG. 51 is small in both of the front direction and the oblique direction. This means that the light control plate 50 is in a state of scattering light irrespective of the incidence angle if rotated about the A-A axis. The linear transmitting light quantity expressed by the broken line in FIG. 51 becomes smaller in the directions close to an incidence angle of 0°. This means that the light control plate 50 is also in a state of scattering light in the front direction when rotated about the B-B axis. Further, in the directions at large incidence angles, the linear transmitting light quantity increases. This means that the light control plate 50 is in a state of transmitting light in an oblique direction when rotated about the B-B axis.
As mentioned above, the previous light control plates show the anisotropic scattering property (property in which the scattering property varies depending on the incidence angle) only in a specific azimuth, and therefore the effect of improving the viewing angle dependency is obtained only in the specific azimuth. In other azimuths, the display quality is reduced because in other azimuths, incident light in an oblique direction is substantially uniformly scattered regardless of the incident angle. In such a respect, the previous light control plates have room for improvement.